High pressure pump



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Jan. 29, 1957 w. R. D. MANNING 2,779,295

HIGH PRESSURE PUMP Filed Jan. 15, 1952 FIG. 2

INVENTOR WILUAM REGINALD DERMOT MANNING ATTORNEYS United States Patent man PRESSURE PUMP William Reginald Dermot Manning, St. Albans, England, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain Application January 15, 1952, Serial No. 266,534

Claims priority, application Great Britain January 31, 1951 2 Claims. (Cl. 103-158) This invention relates to pumps or compressors capable of generating pressures greater than 1,000 atmospheres.

Such pumps or compressors are used in chemical processes where fluid materials are subjected to high pressures such as, for example, in the polymerisation of ethylene.

In pumps or compressors previously used for generating pressures of the order of 1,000 atmospheres or more, it has been found that there is serious risk of failure by fatigue. Such failures have been found to occur at some irregularity of the section such as the valve passages in the cylinder head, or in the attachment of the head to the parallel portion of the cylinder. The occurrence of a failure at such high pressures might well have serious consequences, and one expedient which has been used to avoid such an occurrence is the replacement of the cylinder head after a predetermined number of strokes.

It is the object of this invention to reduce this danger very greatly by superimposing hydrostatic compression at all points where local high and indeterminate tensile stresses may occur which are likely to lead to failure by fiatigue.

According to the present invention this object is achieved by a reciprocating pump or compressor in which the reciprocating action is provided by movement of the cylinder or cylinders and in which the suction and delivery leads of the pump or compressor pass through the piston or each through a piston and the valves for these ducts are at the free ends of the piston or pistons and in which the cylinders are of such shapes that the stresses can be accurately computed. T-rue geometric cylinders with hemispherical ends are preferred.

If the available material is strong enough and the permissible dimensions are suflicient, to contain the required pressure without producing stresses (as calculated by the Lam hypothesis) that exceed the fatigue limit, simple monobloc cylinders can be safely used. For higher pressures it may be necessary to resort to some method of reinforcement such as making the cylinders in concentric parts and shrinking them together, or Wire winding the core tubes, but care must be taken with both methods to avoid over-straining the material during construction. For the former, the most economical vdesign procedure is described in Engineering, vol. 163, No. 4,240, page 349, May 2, 1947, but care must be taken to see that the residual stresses are not too high, and this can be done by using the method described in Engineering of December 8, 1950, in an article entitled Residual Contact Stresses in Built-up Cylinders.

'Figure 1 is a longitudinal, sectional, somewhat diagrammatic view of a pump embodying this invention.

Figure 2 is a view corresponding to Figure 1 of a modified form of pump embodying this invention.

One form of our invention is illustrated in Figure 1 of the accompanying drawing which represents a midsectional elevation of a singlestage pump or compressor comprising a piston and a cylinder. The means for operating and supporting the pump are not shown.

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ducts 6 and 7 and the inlet and outlet non-return valves 8 and 9 which can be of the conventional cone type.

A gland and packing 4 is provided to form a seal between the piston and cylinder.

It is to be understood that the exact type of gland or valve to be used would be chosen according to the working substance and the conditions of operation, e. g. pressure, temperature, running speed. The requirements of the gland are just the same as those that would have to be met with a pump or compressor of conventional type.

Another type of pump or compressor according to the present invention is shown in mid-sectional elevation in Figure 2. This represents a two-stage pump or compressor in which the reciprocating cylinder is 'built up from two axially symmetrical components. In this type of pump or compressor a compound cylinder is preferred in order to reduce tensile stresses about the valve between the chambers. The inner component 1 has two chambers 9 and 10 connected by 'a duct in which a conventional non-return cone type valve 7 is located. Chamber 10 is of larger diameter than chamber 9.

A piston 4 is located in chamber 9 and a seal is provided by the gland 3. A second piston 6 is similarly located in chamber 10. Each piston has a central duct for conveying fluid material and a non-return valve of conventional cone type (5 and 8). The two pistons are mounted on the same axis and the cylinder i arranged to reciprocate over them.

In operating the pump or compressor, when the cylinder moves from the right hand end of its travel towards the left, valve 8 opens and fluid material is drawn into chamber 10. At the same time the fluid material present in chamber 9 is compressed and delivered through valve 5 to the outlet side of the pump. On the return stroke, as the cylinder moves to the right, the fluid material in chamber 10 passes through valve 7, into chamber 9. Since chamber 9 is smaller than chamber 10 this transfer will involve a rise in pressure of the fluid material.

The compression which takes place in chamber 9 will lead to a rise in temperature in this part of the pump and it is desirable that a suitable cooling means should be provided to prevent an excessive rise in temperature. This may take the form of a cooling jacket surrounding the reciprocating cylinder and through which cold water is passed.

In pumps or compressors of the present invention, by reason of the relatively simple shape of the cylinder head, the stresses present can be calculated with considerable accuracy. At the same time, the stresses in the neighborhood of the valve seats and ducts cannot be calculated with any degree of certainty but since they are predominantly compressive the risk of failure at these points due to fatigue is very greatly reduced.

I claim:

1. A reciprocating pump capable of generating pressures greater than 1,000 atmospheres comprising: a reciprocating cylinder having side walls and a hemispherical end wall continuous with said side walls, said side and end walls being of uniform thicknes and having smooth, uninterrupted exterior surfaces free of projections, the other end of said cylinder being open; a stationary piston mounted in said cylinder and defining therewith a pump chamber; pump inlet and outlet ducts extending through said piston; and pump inlet and outlet valves for said ducts at the inner end of said piston.

2: The structure defined inclaim 1 in which the cylinden compr-isc5s= a=- plurality of concentric parts with the outer parts shrunk onto the inner parts.

References'Git'ed in me file of this patent UNITED' STATES PATENTS 1 ,611,849" Chapman Dec. 21, 1926* 1,798,227 Schaer Mar. 31, 1931' Maniscalco Apr. 19; 1938 10 Serial No. 304,414, Kopf (A. P. C.) mlh1ihd May;

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